diff --git a/maths.hpp b/maths.hpp
index a5c26add..4ff39fc7 100644
--- a/maths.hpp
+++ b/maths.hpp
@@ -60,10 +60,10 @@ unsigned
 digits (const T& value) pure;
 
 
-template <typename T>
+template <typename T, typename U>
 T
-divup (const T a, const T b)
-    { return (a + b - 1) / a; }
+divup (const T a, const U b)
+    { return (a + b - 1) / b; }
 
 
 /**